To prepare sponge, combine first 4 ingredients in a medium bowl, stirring well with a whisk. Cover loosely with plastic wrap; let stand 15 minutes.
To prepare dough, weigh or lightly spoon 75 ounces (about 1 1/2 cups) all-purpose flour and pastry flour into dry measuring cups; level with a knife. Combine 1/4 cup sugar, sour cream, butter, salt, vanilla, 1 egg, and sponge in a large bowl; beat with a mixer at medium speed 1 minute or until well combined. Add flours; beat at low speed 3 minutes or until a soft dough forms. Turn dough out onto a lightly floured surface. Knead until smooth and elastic (about 4 minutes), adding remaining 15 ounces all-purpose flour, 1 tablespoon at a time, to prevent dough from sticking. Place dough in a large bowl coated with cooking spray. Cover and let rise in a warm place (85°), free from drafts, 1 hour and 15 minutes or until doubled in size. (Gently press two fingers into dough. If indention remains, dough has risen enough.)
To prepare filling, combine cream cheese and the next 4 ingredients (through dash of salt) in a medium bowl; beat with a mixer at medium speed until smooth.
Punch dough down; roll dough into a 12 x 15-inch rectangle on lightly floured parchment paper. Spread cream cheese mixture down center of dough, leaving about a 5-inch border on each side and a 1-inch border at top and bottom of rectangle. Make 5-inch cuts about 1 inch apart on both sides of dough to meet filling using a sharp knife or kitchen shears. Remove 4 outer corner strips of dough from rectangle; discard. Fold top and bottom 1-inch portions of dough over filling. Fold strips over filling, alternating strips diagonally over filling. Press ends to seal. Transfer braid and parchment paper to a baking sheet. Cover and let rise 45 minutes.
Preheat oven to 375°. Combine 1 teaspoon water and 1 egg; stir with a whisk. Brush braid with egg mixture. Bake at 375° for 20 minutes or until golden. Cool on wire rack 10 minutes.
Combine powdered sugar and 2 teaspoons milk in a bowl, stirring until smooth. Drizzle glaze over braid; sprinkle with nuts.